The present invention relates to disc brakes for vehicles, and in particular to an arrangement for connecting a brake disc to an axle hub, including axle hubs utilized on commercial vehicles, such as tractor-trailer trucks, box trucks, buses, and the like.
Disc brakes are increasingly being used on commercial vehicles, replacing conventional drum brakes. Due to the very high braking forces (aka braking loads) generated when the disc brake's caliper applies the brake pads to the brake disc to slow such heavy vehicles, very robust and often complicated designs have been required to connect the brake disc to the axle hub to transfer the braking forces from the brake disc to the axle hub on which the brake disc is mounted. The design of the brake disc-to-hub connection is further complicated by the heat generated during braking as the kinetic energy of the vehicle is converted into heat energy by application of the brake pads to the brake disc. This heat can be detrimental to the axle hub and its components (such as bearings and seals), as well as to other adjacent components that may receive heat from the axle hub as the hub receives and dissipates the heat received from the brake disc.
Commercial vehicle brake discs, also referred to as “brake rotors” or “rotors,” often are mounted onto axle hubs using so-called spline arrangements using a fixed or floating connection, such as taught in U.S. Pat. Nos. 6,626,273 and 7,410,036. One example is the Splined Disc® brake assembly from Bendix Spicer Foundation Brake LLC. These types of brakes typically are mounted on an axle hub having a plurality of axially-oriented splines arranged around an outer circumference of a disc-mounting region of the hub. The splined disc has corresponding radially-inward facing tabs about the inner circumference of the hub mounting portion of the brake disc. The disc is typically mounted to the axle hub by axially sliding the brake disc onto the hub's mating splines, followed by insertion and/or attachment of a variety of fasteners, brackets, etc., as necessary per the particular splined disc's design in order to secure the brake disc against axial movement off of the hub. When so mounted, the brake disc tabs engage the hub splines in a manner which permits the very large braking forces generated by the disc brake to be transferred to the axle hub and hence to the axle to slow the vehicle. This often requires costly precision machining of the spline/tab engagement surfaces to ensure satisfactory transfer of braking loads in the circumferential direction over the life of the brake disc.
Splined discs typically have had substantial metal-to-metal contact between the inner radial tabs of the brake disc and either the faces of the axle hub splines or intermediary inserts that are used to transfer the braking loads from the disc tabs to the hub splines. The intermediate inserts are used in conjunction with hub axial rotor stop to axially restrain the brake disc on the axle hub. This metal-to-metal contact has the disadvantage of facilitating transfer of a large amount of brake heat from the brake disc directly to the axle hub. This is a particular problem where the axle hub is formed from Aluminum, a material which is being more frequently used for axle hubs in order to minimize vehicle weight and improve fuel economy.
Further, where intermediary disc-to-hub elements are used to locate and transfer brake forces, these typically stainless steel elements add to manufacturing costs, add complication to installation techniques, and are subjected to braking force loads that are high enough to approach the material's durability limits. The excessive heat transferred to the intermediary elements can also raise the temperatures of these elements to a point that long-term strength and fatigue life may be adversely affected.